| Poplar has high value of wide distribution and perfect market prospects as a kind of cultivation tree and timber material in afforestation and woody production. It is playing an important role in changing the ecological environment due to its various good qualities. Compared with other woody plants, poplar has some special characteristics, such as short vegetative cycle, easy regeneration by explants, simple genetic background, etc., so it is treated as the model plant in woody types. With the development of tissue culture and genetic engineering of many woody plant species recent years, biotechniques in various poplar species have made much progress, and some of the transgenic poplars have been in application. It should be a good choice for the salina land of the large northern and western area in China, but the salt-resistance of poplars are not very satisfied. Salt stress is the major factor that limits and decreases the output of crops in many parts of the world, particularly irrigated land. Today, about 20% of the world's cultivated land and nearly half of all irrigated land are affected by salinity. NHX is a tonoplast Na+/H+ antiporter. An active is to sequester Na+ into the vacuole, which results in avoidance of cytoplasmic Na+ toxicity. And at the same time vacuolar Na~+ would serve as an osmoticum necessary for cellular homeostasis. It's one of the fundamental mechanisms of salt tolerance. Advances in molecular genetics and plant transformation have made it feasible to assess biotechnological strategies in improving the salt tolerance of crops, keeping steady-state growth and increasing the output in the saline environment. Overexpressing NHX gene can improve salt tolerance in the transgenic Arabadopsis, oilseed and tomato. Poplar—Zhonglinmeihe was a new poplar cultivar which was developed by Chinese Academy of Forestry with two parental materials. It possesses some good qualities, such as fast-growing, cold tolerance, disease and pest resistance et al.. Besides, it's also a kind of high quality material of wood—pulp and feed. However, it has some characters need to be improved, such as salt tolerance. In this thesis, we employed Poplar—Zhonglinmeihe as material, the goal is to establish the tissue culture and plant regeneration system, then transformed salt-tolerant gene ---NHX gene which was isolated from local halophytic plant in Xinjiang into Poplar—Zhonglinmeihe, to increase its capability in salt tolerance. In this study, young stems, leaves and petioles were used as explants. The results showed that the adventitious shoots inducing rate of petioles were higher than leaves and stems. Shoots rate of stem cambium layer was also good, but stem cambium layer cultivated by water for a long time was difficult to be sterilied. The optimal medium of the primary culture of the explants was 1/2MS + 6-BA0.5 mg·L-1 + NAA0.05 mg·L-1 , in here, the basic medium of 1/2MS was better than MS. The rate of adventitious shoot inducing was 76%. Shoot number was 4.7% per petiole. The best medium of subculture was 1/2MS + 6-BA0.3 mg·L-1 + NAA0.05 mg·L-1. The optimal medium of rooting was 1/2MS + IBA 0.05 mg·L-1+15g·L-1 sugar +8 g·L-1agar.The survival rate of transplantation of the regeneration plantlet was high. The establishment of tissue culture and regeneration system of Poplar—Zhonglinmeihe lay a solid fundation for its rapid regeneration and genetic transformation. Based on the tissue culture system of Poplar-zhonglinmeihe, the NHX gene was introduced by Agrobacterium tumefaciens---mediated method. Meantime, some major factors which influence on the genetic transformation were investigated. The results showed that precultured for 1 day of young stem explant was observed as the best physical and transformation condition; when the bacterium concentration reached OD600=0.3, infection time 15-30min was the best combination; co-culture medium supplied with 200 umol/L AS was suitable. After sometime on the selection medium, the rate of Kan resistant shoots was 25%. By PCR test, some Kan resistant platlets were PCR positive and was preliminarily proved that NHX gene had integrated into genomic DNA. The establishment of transformation system had high significance both in theoretical and technical aspects of poplar—Zhonglinmeihe.
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